Language and communicative impairments following stroke (aphasia) affect more than 30% of stroke survivors, with an incidence of over 180,000 new cases annually. The consequences of aphasia are far reaching and can affect psychosocial adjustment, family role participation, vocational opportunities, and the ability to function independently in society. Recent estimates suggest that VHA outpatient clinics see 2000 new cases of aphasia each year, meaning that approximately 20,000 enrolled VHA patients and 100,000 United States Veterans are currently living with the condition. In response to this need, the VA Pittsburgh Healthcare System Geriatric Research, Education, and Clinical Center (GRECC) initiated the Program for Intensive Residential Aphasia Treatment and Education (PIRATE) in January 2009. PIRATE is a clinical demonstration project that provides approximately 100 hours of cognitive- linguistically oriented aphasia treatment to community dwelling Veterans over a 4-week period. PIRATE currently serves 18 Veterans per year in bi-monthly sessions. Resource limitations associated with PIRATE and aphasia treatment in general require that treatments be offered in the most cost-effective doses to those Veterans most likely to benefit from them. The proposed treatment-effectiveness research addresses these issues by examining the dose-response relationship for semantically-oriented naming treatment, and identifying cognitive, psycholinguistic and neuroanatomical predictors of treatment success. Study participants (n=50, over a 4-year period) will be recruited nationwide from Veterans enrolled in PIRATE. They will have their naming performance measured prior to PIRATE entry, during each week of treatment, and at program exit/follow-up. A battery of cognitive measures and structural magnetic resonance images of their brains will also be collected prior to treatment. Participants' performance on trained and untrained lexical items and a standardized measure of naming performance will be compared across time intervals to specify the therapy amounts for which maximum treatment benefits are achieved. Their treatment outcomes will also be correlated with specific cognitive test scores and the location and extent of their brain lesions to identify cognitive and neurological markers predictive of positive treatment response. Treatment response will also be compared across participants with different psycholinguistic profiles, to determine which groups of patients show greatest benefit from semantically-oriented naming treatment. The proposed research should provide answers to two interlocking questions: for whom is aphasia therapy most effective, and how much of it is needed to optimize treatment outcomes. These answers have the potential to set transformative new standards for how aphasia treatment is delivered within VHA.